Biomimetic Synthesis of Litebamine

Treatment of the isoquinolinium methiodide 1 with sodium methoxide in methanol for two hours at reflux temperature gave the tetrahydroisoquinoline 2 in quantitative yield, and not the anticipated benzazepine 3. This unexpected result was then exploited as follows for a biomimetic synthesis of the alkaloid litebamine. Thus, quaternisation of (S)-0,0-diacetylboldine 4 with iodoacetonitrile in methylene chloride (41%) followed by treatment of the salt with NaOMe/MeOH gave litebamine 5 (69%). 

Give mechanisms for the transformations of 1 into 2 and of 4 into 5, and explain on a mechanistic basis why 3 was initially expected to be the product obtained from treatment of 1 with base. 

Give a mechanism for the formation of this latter compound. 

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